The trial of a 72-year-old American man whom Russia accuses of working as a mercenary for Ukraine will take place behind closed doors and the verdict will be announced next Monday, Russian state media reported.

Stephen Hubbard is accused of signing a $1,000 per month contract with a Ukrainian territorial defense unit in the city of Izyum in February 2022. He was captured by Russian forces in April that year, and faces a sentence of seven to 15 years if convicted.

The RIA news agency said the judge on Thursday accepted a prosecutor's request to hold the proceedings in secret to ensure the safety of the participants. It was not clear why the prosecutor believed an open trial would have placed them at risk.

RIA said Hubbard himself supported the move, saying he did not want outsiders to be present. RIA reported earlier that he had pleaded guilty to the charges. Another state agency, TASS, said the verdict would come on Oct. 7.

A U.S. embassy spokesperson said: "We are aware of reports of the arrest of an American citizen. Due to privacy restrictions we are unable to comment any further."

Prosecutors have said Hubbard was provided with training, weapons, and ammunition when he allegedly signed up.

Hubbard's sister Patricia Fox and another relative have cast doubt on his reported confession, saying he held pro-Russian views and was unlikely to have taken up arms at his age.

"He never had a gun, owned a gun, done any of that... He's more of a pacifist," Fox told Reuters last month.

Hubbard is one of at least 10 U.S. nationals behind bars in Russia over two months after a prisoner swap between Moscow and the West on Aug. 1 freed 24 people, including three Americans.